If either of the fins is true, which candidates can I eliminate?Ģ. The player must then analyze two options:ġ. The fins in this case will be the extra positions for the digit. However, when the extra possibilities for the digit are restricted to one group, the player has a Finned X-Wing pattern. Sometimes, one of the vertices of the rectangle/square is missing because the digit is a candidate to more cells in that row/column and the 2 by 2 requirement of the X-Wing pattern is not met. Throughout the puzzle, it is usual for the player to find incomplete Sudoku X-Wing patterns. Thus, the 8 circled in red between the two highlighted yellow cells at the bottom can be eliminated. Trying both configurations reveals that, regardless of the final answer, the number 8 cannot be a candidate in the rows connecting to the base pattern. If the two 8 connected by the dotted line are true, the other pair becomes false and vice-versa.

Since these 4 cells are aligned by column and row, it is possible to apply the Sudoku X-Wing technique. In the example above, it is clear that the number 8 has only two possible solutions within the highlighted columns. Practical exampleĪccording to the basic rules of Sudoku, every row and column must contain the numbers from 1 to 9 without repetitions. Likewise, with X-Wing patterns on columns, it is impossible for the digit to be a candidate in the rows connected to the base pattern. That is, the pairs formed by the cells diagonally opposite to one another.īy testing each set of possibilities on the grid, it becomes clear that whenever the Sudoku X-Wing technique is applied to rows, the digit in analysis cannot be a candidate to any cell of the columns connected to the base cells. Since the digit has only two possible solutions in the rows or columns in analysis and each cell is directly affected by the others, the player can identify only two possible sets of solutions for the digit. The basic principle of this technique is simple. These cells must be aligned by column and row, forming a square or rectangle when connected. To be able to apply this technique, the player must find 2 rows or 2 columns where a single digit is a candidate in only two cells of each.

Requirements to apply the Sudoku X-Wing strategy Together with the Swordfish, the Sudoku-X-Wing technique is also a valuable strategy for any player to learn as it branches out into more complex patterns and techniques that are required to solve impossible puzzles. It focuses on one single digit and its goal is to restrict the number of cells that can have that number as a possible candidate. It is a very straightforward technique with an easily identifiable pattern. The Sudoku X-Wing strategy is one of the most recurrent techniques that can be applied to Sudoku puzzles from a medium difficulty level onwards.

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